Preadipocyte factor 1 (pref- 1) is a transmembrane protein that contains epidermal growth factor-like repeats. Pref- 1 can be cleaved to generate a soluble factor. Using differential screening ,the investigators originally cloned pref-l from embryonally- derived 3T3-Ll cells. The correlative observations suggest a role for pref- 1 during growth and differentiation of islet 3-cells. The specific aims of this exploratory grant proposal are: 1) To demonstrate pref- I function in 13-cell growth and differentiation by generating transgenic mice overexpressing pref- 1 driven by the insulin promoter. 2) To examine the effect of pref- 1 during in differentiation and growth of AR42J cells into insulin-positive endocrine cells.